Xerographic fusing apparatus



P. G. ANDRUS ETAL 3,356,831

XEROGRAPHIC FUSING APPARATUS I Filed Dec. 23, 1964 FIG. 4

A ram/5 rs Dec. 5, .1967 P. G. ANDRUS ETAL 3,

XEROGRAPHIC FUSING- APPARATUS 5 Sheets-Sheet Filed Dec. 23, 1964 ATTORNEYS Dec. 5, 1967 P. G. ANDRUS ETAL XEROGRAPH IC FUSING APPARATUS Filed Dec.

5 Sheets-Sheet 3 ATTORNEYS United States Patent ()fiFrce 3,356,831 Patented Dec. 5, 1967 3,356,831 XEROGRAPHIC FUSING APPARATUS Paul G. Andrus, Powell, and John F. Byrne, Columbus, Ohio, and Frederick W. Hudson, West Henrietta, N.Y., assignors, by direct and mesne assignments, to Xerox gorporation, Rochester, N.Y., a corporation of New ork Filed Dec. 23, 1964, Ser. No. 420,687 11 Claims. (Cl. 219-388) ABSTRACT OF THE DISCLOSURE An apparatus for fixing xerographic toner powder to a support surface including a source of heat positioned in thermal contact with a toner-powder-bearing support surface for fusing the image, and a heat exchanging unit to transfer heat from the fused support surface to the support surface prior to entering into thermal contact with the source of heat for preheating the support surface thereby lowering the amount of energy required by the heat source for fusing.

This invention relates to xerography and, in particular, to improved fusing apparatus for afiixing xerog-raphic powder images onto a moving support surface. More specifically, the invention relates to an improved heat fusing apparatus having a greater thermal efficiency than prior art devices.

In the process of xerography, for example, as disclosed in Carlson Patent No. 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged finely divided material, such as an electroscopic powder, that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrost-atic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface to which it may be affixed by any suitable means.

The application of heat to aflix xerographic powder images to support surfaces has been extensively employed. Typical heat fusing apparatus for affixing powder images to moving support surfaces is disclosed in Crumrine Patent No. 2,852,651. Most fusing apparatus of the prior art consume electrical input energy that is converted into heat to be emitted as radiation, convection, conduction or a combination thereof. The powder image on its support is passing through or past the apparatus is heated sufficiently to soften the powder which, on cooling, affixes itself to the support surface. The tenacity or degree of bond with which the powder image adheres to the support surface to render it commercially acceptable is that which will generally not be subject to finger smearing. Also it should generally be resistant to mechanical abrasion, approximating the effect of normal document use as is known in the art.

It has been calculated that under optimum fusing conditions a powder image should be fused on to a support surface to commercial standards using an electrical energy input of about 17 watt-seconds per square inch of support surface. This optimum condition based on an average image area, presumes that the total thermal energy produced from the electrical input is consumed and confined solely for the heating of the loose powder image. Fusing is commonly accomplished by heating the paper or other moving support surface carrying the powder image, and the theoretical optimum presumes this is achieved without loss of such heat to parts of the heat fusing apparatus. The only heat lost in this optimum condition would be that to the ambient air by the absorbed heat of moving support surface as it leaves the apparatus.

An inherent limitation in fusing devices of the prior art has been the consumption of electrical input energy greatly in excess of the theoretical optimum low, being generally in the range of 60 to 70 watt-seconds per square inch of support surface to meet commercial standards. A major part of this inefficiency is attributed to the inability to confine the heat to the imaging powder or its support such that the excess energy consumed represents an economic loss to the consumer. Despite the recognition of this inefficiency it has not been possible in accordance with the construction of prior art devices to affect control or reduction of this heat loss. It should be apparent, therefore, that direct economic savings would be immediately available wit-h a heat fusing apparatus capable of substantially greater efiiciency than prior art devices approaching and even surpassing 17 watt-seconds per square inch of copy sheet.

Now, in accordance with the present invention there is provided apparatus whereby loose powder images on a moving support surface may be atfixed to commercial standards, using substantially less input energy than was previously known in the art, and even less than the theoretical optimum stated above. Specifically, with the de vice hereof it has been possible to afiix loose powder images to commercial standards consuming an average energy input of about 10 watt-seconds per square inch of support surface. The advantages, including economic, afforded by the device hereof should be readily apparent.

Thus, it is an object of the invention to provide an improved heat fusing apparatus for affixing a loose powder image onto a moving support surface having increased thermal efiiciency than heretofore.

It is a further object of the invention to improve heat fusing apparatus for affixing a loose powder image onto a moving support surface with a reduced energy input necessary to meet commercial fusing standards as to effect a decrease in operting cost.

These and other objects of the invention are achieved by the improved fusing apparatus of the invention having a heating platen and a heat exchange unit over which passes the image bearing support surface. The heat ex change unit is effective to transfer heat by conduction from the exiting to approaching portions of the support surface prior to contact of the approaching areas with the heating platen. By this means, heat contained in the exiting portion and which previously has been lost to the ambient air, is conducted back to the web portions which are approaching the heating platen to effect preheating of these areas. This preheating brings the support to a temperature below fusing and reduces the amount of heat necessarily supplied for fusing from the heating platen.

For a better understanding of the invention, as well as other objects and further features thereof, a reference is' FIG. 4 is a sectional elevation of the fusing apparatus taken substantially along line 44 of FIG. 2.

For a general understanding of the xerographic processing system in which the invention is incorporated, reference is had to FIG. 1 in which the various system components are schematically illustrated. As in all xerographic systems based on the concept disclosed in the above-cited Carlson patent, a radiation image of copy to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image corresponding to the latent image on the plate surface. The powder image is then electrostatically transfered to a support surface to which it may be afiixed by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the xerographic apparatus shown, original copy to be reproduced is placed on a support tray from which it is fed onto a feed apparatus generally designated 11. On the feed apparatus the original is moved on an endless belt 12, driven by motor 13, to pass the optical axis of projection lens system 14 that is illuminated by a projection lamp LMP-l. The image of the original is reflected by mirror 15 through an adjustable objective lens 16 and then reflected by mirror 17 downwardly through a variable slit aperture assembly 18 and onto the surface of a xerographic plate in the form of a drum 19.

Xerographic drum 19 includes a cylindrical member mounted in suitable hearings in the frame of the machine and is driven in a clockwise direction by a motor 24 at a constant rate that is proportional to the transport rate of the original, whereby the peripheral rate of the drum surface is identical to the rate of movement of the projected radiation image. The drum surface comprises a layer of photoconductive material on a conductive backing that is sensitized prior to exposure by means of a corona generating device 25, which may be an adaption of the type disclosed in Vyverberg Patent No. 2,836,725, that is energized from a suitable high potential source.

The exposure of the drum to the radiation image discharges the photoconductive layer in the areas struck by radiation, whereby there remains on the drum. a latent electrostatic image in image configuration corresponding to the radiation image projected from the original. As the drum surface continues its movement, the electrostatic latent image passes through a developing station 26 in which a two-component developer material 27, which may be of the type disclosed in Walkup Patent No. 2,638,416, is cascaded over the drum surface by means of developing apparatus 28.

In the developing apparatus developing material is carried up by conveyor 29, driven by suitable drive means from motor 30, and then released onto chute 31 whereby it cascaded down over the drum surface. The toner component 32 of the developer that is consumed in developing is stored in dispenser 33 and is dispensed in amounts controlled by gate 34.

After developing, the xerographic powder image passes a discharge station 41 at which the drum surface is illuminated by lamp LMP-2, whereby residual charges on the non-image areas of the drum surface are completely discharged. Thereafter, the powder image passes through an image transfer station 42 at which the powder image is electrostatically transferred to a moving support surface 43 by means of a second corona generating device 44 similar to corona charging device 25, mentioned above.

The moving support surface 43 to which the powder image is transferred may be of any convenient type, such as paper, and may be obtained from a supply roll 45, fed over guide roll 46 and over suitable tensioning rolls being directed into surface contact with the drum in the immediate vicinity of transfer corona generating device 44. After transfer, the support surface 43 is separated from the drum surface and guided through the fusing apparatus of the invention, generally designated 48, wherein the powder image is permanently aflixed thereto. Thereafter, the support surface may be fed over a further system of guide and tensioning rolls and onto a takeup roll 52 that is driven by motor 53.

After separation of the support surface 43 from the drum, a corona generating device 54 directs electrostatic charge to a residual powder image on the drum surface. Thereafter, the xerographic drum surface passes through a cleaning station 55 at which its surface is brushed by a cleaning brush assembly 56, rotated by a motor 57, whereby residual developing material remaining on the drum surface is removed. The drum surface then passes through a second discharge station 58 at which it is illuminated by fluorescent lamp LMP-3, whereby the drum surface in this region is completely flooded with light to remove any electrostatic charge that may remain thereon. Suitable light traps are provided in the system to prevent any light rays from reaching the drum surface, other than the projected image, during the period of drum travel immediately prior to sensitization by corona generating device 25 until after the drum surface is completely passed through the developing station 26.

The fusing apparatus 48 of the invention will be described with reference also to FIGS. 2, 3, and 4. During operation of the xerographic apparatus, the image bearing support surface 43 carrying the loose powder image 90 is moved through the fusing apparatus in a path accorded by the interrelation of entrancing guide roller 60, heating platen 61 exiting guide roller 62, and heat exchange unit 66.

For support and insulation of the components, the fusing apparatus 48 includes a frame 64 formed of a pair of opposite side walls 80 and 81 secured via an end plate 82 and bottom plate 85. The frame is in turn supported in the xerographic apparatus adjacent the path of movement of the support surface 43 by a bracket 89 spanning below the frame 'for connection to the xerographic apparatus. The sides 80 and 81 are of a thermal insulating material of sufiicient thickness and durability, for example, a inch thick phenolic material, to form a thermal insulating barrier between the heat fuser and ambient air and to support the heat exchange unit. The exchange unit is attached in such a relation to the entrancing roller 60, the heated roller 61 and the exiting roller 62 to allow the entire width of the moving support surface 43 to pass in direct and thermal contact over the length and the width of the heat transfer ribs, as will be described.

Forwardly supported within the frame is a heating platen in the form of a roller 61 mounted for rotation, and behind which is a heat exchange unit 66 both substantially enclosed by a closely spaced thermally insulating shroud comprising a pivot movable top plate 71 connected by hinge to a bottom plate 72. Top plate 71 is secure-d in operating position by thumb latch 76, such that both plates are a sufficient distance, for example, M1. inch from the moving support surface 43 as it travels across the surface of the heat exchange unit and heated roller to closely confine the heat and yet avoid disturbance of the loose powder image 90 carried thereon. Both top and bottom plates 71 and 72 respectively are constructed to be thermal insulating comprised, for example, of fiberglass batt 74 between two secured metal shields 73. They are shaped to conform to the side plates and 81 of the frame 64 and define a passage to allow a moving support surface to pass in contact with the heat exchange unit and the heating platen. As the support surface 43 moves under tension past roller 60, about platen 61 and to the exiting roller 62, the under surface thereby is maintained in direct thermal contact with heat exchange unit 66 which effects a conductive heat exchange from portions of the support surface 43 subsequent to contact with the heating platen 61 5. to portions of the support surface 43 approaching contact with the heating platen 61.

The primary source of heat is provided by a heating platen in the form of a roller 61. The roller 61 is a mechanically hard, firm heat conductive material such as drawn copper tube formed with a inch wall 68 and containing a coaxial electrical heating element 69 extending coextensive therewith for heating the periphery to the required temperature. The tube is of a length approximating the width of the moving support surface 43 and the heat exchange unit 66. The heating element 69 is a commercially available inch diameter, 115-125 volt, 500 watt infrared heating element, extending the length of the copper -wall 68 and is connected to a 500 watt, 115-125 volt power source 86 at a terminal 88 on an electrically insulating block 87.

The heat exchange unit is secured to frame 64 via side bolts 97 and 98 and is comprised of a plurality of sequentially arranged heat transfer ribs 91 through 96 separated and alternated by a plurality of thermally insulating ribs 67, held together to form one unit by two bolts 83 extending laterally through the ribs. The heat transfer ribs 91 through 96 are constructed of a solid thermally conductive material such as aluminum being substantially rectangular in cross section and individually decreasing in height with the proximity from the platen 61. The thermal insulating ribs 67 comprise substantially rectangular solids of a thermal insulating material such as Teflon about inch in thickness. The seven insulating ribs 67 and six heat transfer ribs 91 through 96 are arranged alternately with an insulating rib being at each end of the heat exchange unit 66 taken in the direction parallel to the path of the moving support surface 43. Completely covering the 13 ribs along both side edges in order to prevent heat loss therefrom are thermal insulatingblocks '77 of Teflon or the like. As can be seen, the ribs terminate top and bottom shaped to form a smooth continuous contoured surface for contact by the moving support. By constructing the heat exchange unit in this manner, i.e., with alternating heat conductive and insulating ribs, there is achieved maximum heat exchange capacity as opposed to one unitary heat transfer member. With this arrangement rib 1 is in thermal contact between the hottest portion of the exiting web along its bottom edge and the warmest portion of the entering web, along its top edge. At the same time rib 96 is in thermal contact between the relatively cooler portion of the existing web along its bottom edge and the coldest, completely unheated portion of the entering web along its top edge. By contrast a unitary solid heat transfer member, although operable in accordance herewith, achieves a uniform temperature for transfer of heat to and from all portions of the web as to be less efiicient in its exchange of heat.

The following measurement data exemplifies operation of the heat exchange unit during a period of operation with the heated roller 61 at a temperature of about 312 F. The temperatures of the heat transfer ribs were measured by thermometers placed in thermometer wells 78 extending into the center of each rib. Transfer rib 91 was recorded to be 252 F., rib 92 250 F., rib 93 243 F., rib 94 232 F., rib 95 212 F., and rib 96 was recorded to be 174 F. From these readings it is apparent that the heat transfer ribs are effective to extract heat from the support surface along their bottom edges to pre-heat portions of the support surface along their top edges. Heat transfer rib 91 has the highest temperature because the support surface immediately subsequent to contact with the heating platen is the hottest. Also, heat transfer rib 91 transfers this heat to portions of the support surface immediately prior to their contact with the heating platen 61, following contact of these same portions with heat transfer ribs 92 through 96 having already pre-heated the moving support surface to a substantial degree. Heat transfer rib 96 has the lowest temperature because it transfers heat from portions of the support surface which have already had heat transferred by heat transfer ribs 91 through 95. Thus, the desirable result is achieved of having the support surface immediately prior to its contact with the heating platen being heated toa high temperature while support surface, subsequent to contact with the heating platen at transfer rib 96 immediately prior to its exit from the heat fusing apparatus to the ambient air has been cooled to a relatively low temperature.

Each of the support surface guides, 60, 61, and 62 are supported for rotation by having their ends fitted into bushings 84 suitably placed inside the side walls of the frame 64 or the frame of the copying apparatus. The lengths of the rollers are substantially coextensive with the internal dimensions of the frame at least sufficient to support the width of the moving support surface.

In operation an image-bearing moving support surface 43 before and after passing over the heated roller 61, passes in direct and thermal contact with the top and bottom face respectively of heat exchange unit 66 before leaving the fusing apparatus over the exiting roller. The moving support surface passes out of the heat fusing apparatus 48 and is then wound on takeup roll 52, the loose powder image 99 or images having been afiixed to the moving support surface 43. Because of the improved apparatus of this invention the fixing of the loose powder images to the moving support surface 43, to a commercially acceptable standard is achieved using less input energy than was previously known in the art.

While the invention has been described with reference to the details and construction herein illustrated, it is not confined to the exact mechanism shown. This application is intended to cover such modifications or departures as may come Within the purposes of the invention and the scope of the following claims.

What is claimed is:

1. In a xerographic reproducing unit wherein powder images are loosely supported on a moving support sur face, a heat fusing apparatus for fixing a powder image to said support surface, said heat fusing apparatus comprising in combination:

(a) heating means in thermal contact with the moving support surface to effect fusing of the powder image thereon, and

(b) a heat exchange unit including thermal transfer means supported in heat exchange relation between portions of the moving support surface approaching and past contact with said heating means to transfer heat from the latter to the former portions of said moving support surface to preheat the approaching support surface.

2. Apparatus according to claim 1 in which said heat exchange unit includes means to control heat exchange between relatively hot and cool portions of the support surface moved past said heating means substantially in heat exchange relation with the relatively warm and cool portions respectively, of the support surface portions approaching said heating means.

3. Apparatus according to claim 1 in which said heat exchange unit is comprised of a plurality of thermally conductive transfer members each separated from its adjacent member by thermal insulation means.

4. Apparatus according to claim 3 in which said heat exchange unit is comprised of a plurality of alternating juxtaposed thermally insulating and thermally conductive bars.

5. In a xerographic reproducing unit wherein powder images are loosely supported on a moving support surface, a heat fusing apparatus for fusing the powder image to said support surface, said heat fusing apparatus comprising in combination:

(a) a support frame mounted in the reproducing unit adjacent the path of movement of a moving support surface on which a powder image is loosely supported,

(b) an electrically energized heating platen in the form of a roll supported for rotation in said frame to conductively heat the moving support surface to a temperature sufficieut to fuse powder images supported thereon,

(c) a heat exchange unit on said support frame adjacent said heated roll extending in heat exchange relation between portions of the moving support surface approaching contact with said roller and portions of the moving support surface past contact with said roll whereby heat is transferred from the latter to the former portions of said support surface to preheat said approaching portions,

(d) first guide means supported by the frame and adapted to direct the support surface approaching said heating platen into thermal contact with said heat exchange unit,

(e) a second guide means supported in the frame and adapted to direct the support surface past said heating platen into thermal contact with said heat exchange unit and,

(f) means to maintain the support surface in thermal contact with the heating element and the heat exchange unit as it passes thereabout.

6. Apparatus according to claim including a thermally insulating shroud supported closely spaced and extending at least about the contacting surfaces of said platen and said heat exchange unit and together therewith defining a passage for said support surface.

7. Apparatus according to claim 6 in which said frame includes a pair of secured, spaced apart, parallel walls and said platen and said heat exchange unit are operatively supported between said walls.

8. Apparatus according to claim 6 in which said heat exchange unit is comprised of a plurality of alternating, juxtaposed, thermally insulating and thermally conductive bars the opposite ends of which form continuous surfaces for support surface contact.

9. In a xerographic reproducing apparatus wherein toner powder images are loosely supported in an image configuration on a support surface, a heat fusing apparatus for permanently fixing the toner powder image to said support surface including heating means positioned adjacent the path of movement of a toner powder bearing support surface in thermal contact therewith to effect permanent fixing of the toner powder image to the support surface, and

a heat exchanger including a thermal input terminal positioned adjacent the path of movement of a toner powder bearing support surface subsequent to thermal contact of said support surface with said heating means and a thermal output terminal positioned adjacent to the path of movement of said toner powder bearing support surface prior to thermal contact of said support surface with said heating means to transfer heat from the former to the latter terminal to preheat the support surface prior to permanently fixing the toner powder image supported thereon.

10. The apparatus of claim 9 wherein said heat exchanger terminals include a plurality of separated heat conductive transfer members positioned in thermal contact with the support surface to define a temperature gradient between each transfer member.

11. The apparatus of claim 10 wherein said heat exchanger terminals are positioned adjacent said heating means and extend into physical contact with the support surface prior and subsequent to thermal contact of the support surface with said heating means to preheat said support surface prior to permanently fixing the toner powder image thereto.

References Cited UNITED STATES PATENTS 1,878,318 9/1932 Pinder 25065.2 X 2,870,312 1/ 1959 Westernelt 219-469 3,239,652 3/1966 Price 219470 X FOREIGN PATENTS 679,533 9/1952 Great Britain.

RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner. 

1. IN A XEROGRAPHIC REPRODUCING UNTI WHEREIN POWDER IMAGES ARE LOOSELY SUPPORTED ON A MOVING SUPPORT SURFACE, A HEAT FUSING APPARATUS FOR FIXING A POWDER IMAGE TO SAID SUPPORT SURFACE, SAID HEAT FUSING APPARATUS COMPRISING IN COMBINATION: (A) HEATING MEANS IN THERMAL CONTACT WITH THE MOVING SUPPORT SURFACE TO EFFECT FUSING OF THE POWDER IMAGE THEREON, AND (B) A HEAT EXCHANGE UNIT INCLUDING THERMAL TRANSFER MEANS SUPPORTED IN HEAT EXCHANGE RELATION BETWEEN PORTIONS OF THE MOVING SUPPORT SURFACE APPROACHING THE PAST CONTACT WITH SAID HEATING MEANS TO TRANSFER HEAT FROM THE LATTER TO THE FORMER PORTIONS OF SAID MOVING SUPPORT SURFACE TO PREHEAT THE APPROACHING SUPPORT SURFACE. 